This invention relates to a margine gear drive having two drive pinions each of which is adapted to be coupled to a propulsion engine and which by way of intermediate or layshaft gears drive a common gear which is adapted to be coupled to a propeller shaft, the common gear, the layshaft gears, and the pinions being disposed in only two planes.
In one known marine gear drive of this kind each of two drive pinions meshes with two intermediate or layshaft gears, each of which is connected by a torsion shaft to a pinion, which in turn meshes with a larger common gear. The drive transmission between the two drive pinions and the larger gear thus comprise a total of four intermediate or layshaft gears, four torsion shafts, and four pinions meshing with the larger common gear. The constructional cost this entails is justified when both propulsion engines normally supply power to the larger gear, and thereby to the propeller shaft, simultaneously. If however in normal operation, at so-called cruising speeds, only one propulsion engine is intended to operate while the second propulsion engine is brought into use only when particularly high power is required, this constructional cost seems too high, particularly if the two propulsion engines differ in respect of power and speed in such a manner that a gear drive with power branching is justified only for the more powerful and faster of them. This is particularly the case with coastguard boats and warships, in which a diesel engine is provided for cruising and a gas turbine for active engagements.
With the abovementioned known gear drive it might appear obvious for such purposes to arrange one drive pinion to mesh only with one intermediate gear and to omit the other intermediate gear together with the associated torsion shaft and the pinion fastened thereon. However, the saving achieved is offset by the disadvantage that for the one drive pinion the drive transmission cannot then be preloaded and it rattles or vibrates when power is supplied only to the other drive pinion from its propulsion engine.
The problem underlying the invention is to improve a marine gear drive of the kind described above, particularly for use in coastguard boats and warships, in such a manner that the number of gears running idle when only one propulsion engine is in use is restricted to a minimum.